Now, in order to solve the differential equation (REF ) with the conditions (REF ), we used the Mashhoon's Method [1]},[2]}. According to this method the QNM's of a potential barrier are
related to the bound states of the inverted potential. The frequency of waves must be complex, \( \omega = \omega _{r} + i\omega _{i}\) . The imaginary and real parts are related to the damping time scale (\(\tau _{i} = 1/\omega _{i}\) ) and oscillation time scale (\(\tau _{r} = 1/\omega _{r}\) ), respectively.
The proper QNM's using this method can be obtained as
\(\omega _{r}=\pm \left(V_{0}-\dfrac{\eta ^2}{4}\right)^{\dfrac{1}{2}},\;\;\;\;\; \omega _{i}=\eta \left(n+\dfrac{1}{2}\right),\) 
